Technological advances have succeeded in continuously reducing the cost of bandwidth, thus spurring the development of new sets of services and transmission technologies deployed alongside older ones, which has resulted in increased levels of heterogeneity in the telecommunication ecosystem. These technologically driven changes in the telecommunication industry have resulted in multiple challenges for communications service providers (CSPs). CSPs have to address the growing need for bandwidth, manage an increasingly heterogeneous network, and maintain the required quality of service (QoS) of its service portfolio, while remaining competitive and profitable.
High-data rate transmissions over optical fiber have demonstrated the undeniable superiority of optical communications in terms of capacity and reach. As a consequence, for data transmissions over few tens of megabits per second and over anything from hundreds of meters and upwards, optical fiber has become the preferred transmission medium, making fiber optics the de facto backbone of the telecommunications and data networking infrastructures. Additionally, optical networks have other advantages beyond contributing enormous capacities to the network. For example, optical networks can provide a common infrastructure over which a variety of services can be delivered. Further, optical networks can, to a certain degree, provide spatio-temporal flexibility in the delivery of bandwidth.
Similar to the telecommunication network as a whole, optical networks have grown more complex over time. Today, fiber-optic-usable bandwidth is extensively utilized based, at least in part, on improvements in spectral efficiency (SE). Because of uninterrupted development in high-speed electronics, advances in fiber optic network optical elements, and the use of advanced signaling techniques, optical communication systems have reached a state of greater signal waveform flexibility and higher single channel data rates that now exceed 200 Gb/s [4]. As a result, the next generation of fiber optic communication systems is leaning towards a larger degree of dynamic adaptability in reach, data rate, and spectral occupancy, thus shifting away from legacy single purpose transceivers.
But optical fiber communication networks have certain limitations. In particular, their lack of mobility and required intensive infrastructures present certain challenges. For example, deploying or redeploying optical fiber is costly, time-consuming, and can be problematic in certain environments such as highly urban areas or extreme geographical locations where infrastructure costs are significant or, in the worst case scenarios, practically impossible.
Conventional microwave radio technology provides a viable alternative to optical fiber communication networks because it is rapid to deploy and suited for mobile and remote environments. It is challenged, however, by the growing data demands of users.
Multi-gigabit wireless photonics enable bridging fiber optic and wireless networks in a seamless fashion via the interposition of a wireless gateway that enables the conversion of optical signals to electrical wireless signals and vice versa. This technology provides the maneuverability and capacity required in some applications since it retains the mobility and deployment ease of wireless while providing fiber optic equivalent capacities and latencies to fixed and mobile users within a coverage area. Accordingly, evolutions in fiber optic network optical elements, high-speed electronics, and the convergence of the optical-wireless network have and will continue to dramatically increase the network's heterogeneity as well as its complexity.
Managing greater heterogeneity and complexity for modern communication networks is feasible with the cooperation of an omniscient supervisory control layer, which ensures coordination between all elements of the network for smoother data transmission from one client site to another. Typically, these architectures require critical transmitter and/or channel information be available at the receiver. For example, to function effectively, such architectures depend on the receiver having maximum foreknowledge of a received signal's transmission parameters such as modulation format, symbol rate (i.e., baud rate or modulation rate), and carrier frequency, as well as the number of the multiplexed polarizations and the length of the signal's transmission over fiber and the type of fiber used in the transmission.
Time-domain hybrid modulation formats (TDHMFs), which can be highly variable, introduce additional challenges in modulation format recognition. As can be appreciated, TDHMFs offer tenability within a continuum of tradeoffs between capacity, spectral occupancy, and reach, but they also increase the complexity of traffic patterns, specifically in the case of transceivers. Generally, to demodulate a received TDHMF signal, the receiver requires knowledge not only of the transmission parameters but also parameters of the TDHMF, in particular, the pattern length, composing modulation formats, their ratio in the pattern, and the pattern arrangement in time.
But there are important situations where network elements are not properly synchronized with the flowing signal despite conventional procedures that the supervisory control layer usually carries to solve such a problem. For example, in certain scenarios (e.g., when the supervisory channel is disrupted or deemed too slow to allow fast and flexible provisioning), the optical receiver either cannot or does not know the properties of the incoming signal and therefore cannot extract the information.
Accordingly, a need exists for a receiver that is capable of identifying and decoding signals, including complex signals, without any or all of the typically required foreknowledge of the signal's parameters.